The present invention relates to a laser beam printer capable of protecting an operator from being exposed to laser beams. FIG. 3 is a sectional view showing the construction of a key portion of a laser beam printer. In FIG. 3, reference numeral 4 designates a laser scanner; 10, a photoreceptor drum cartridge; 10-1, a photoreceptor in the form of a drum; 11, a toner cartridge; 20, a laser beam printer; 21, a pop-up; 22, a fulcrum; and 23, a laser beam path.
A laser beam emitted by the laser scanner 4 travels along the laser beam path 23, and hits the surface of the photoreceptor 10-1, thereby forming a latent electrostatic image thereon. Toner supplied from the toner cartridge 11 is applied to the latent image, to form a toner image. The toner image is transferred to and fused on a recording paper, which is supplied along a paper path 24. The paper bearing the image is forwarded in the direction B, and discharged outside the laser beam printer.
The laser beam printer thus constructed uses consumable parts removably set or attached to the printer, such as the drum cartridge and the toner cartridge. Those parts are frequently removed from the printer body at the time of periodical inspection, replacement of old parts with new ones, repair for jamming, for example. In such a case, the pop-up 21 is raised.
The pop-up 21, which includes some parts of the printer structure, for example, the laser scanner 4, and the like, is upwardly swung about the fulcrum 22 in the direction A. After the pop-up 21 is raised, the inner structure of the laser beam printer is exposed to allow an operator or a serviceman to make an easy access to the inner structure for inspection and repair.
In a state that the printer is turned on, when the consumable part, such as the drum cartridge 10, is removed, the direct or reflected laser beam, which has been interrupted by some parts before removal of the consumable part, appears outside where it could possibly hit the operator. The laser beam is hazardous for the operator. When it hits the eyes of the operator, he may lose his eyesight. To avoid such a dangerous situation, a measure has been taken for shutting off the laser beam when the drum cartridge 10, for example, is removed.
FIG. 5 is a block diagram showing a key portion of the electrical arrangement of a conventional laser beam printer. In FIG. 5, reference numeral 1 indicates a laser-beam emission controller; 2, an interlock switch; 3, a power source; 4, a laser scanner; 5, a laser controller; 6, a CPU (central processing unit); 7, an I/0 (input/output) port; 8, a drum detect switch; 9, a toner detect switch; 10, a drum cartridge; and 11, a toner cartridge.
The interlock switch 2 is provided for checking whether or not the pop-up 21 has been returned to the normal position, and is lit on when the pop-up 21 is returned to the normal position. FIG. 4 is an explanatory diagram showing the on/off operation of the interlock switch 2. In the figure, reference numeral 2-1 designates a spring; 21-1, a pop-up cover; and 21-2, a projection. When the pop-up 21 is at the normal position, the projection 21-2 pushes down the interlock switch 2. When the pop-up 21 is turned in the direction A shown in FIG. 3, the projection 21-2 is apart from the interlock switch 2. The interlock switch 2 is pulled up by the spring 2-1, so that it is turned off. When the switch 2 is turned on (that is, the pop-up 21 is returned to the normal position), electric power is supplied from the power source 3 to the laser controller 5.
The laser controller 5, although power is supplied thereto, will not be operated until the drum cartridge 10 and the toner cartridge 11 are set to the printer. The setting of the cartridges 10 and 11 is detected by the drum detect switch 8 and the toner detect switch 9. The detection is transferred to the laser controller 5, through the I/O port 7 and the CPU 6. The drum detect switch 8 is a mechanical switch, which is turned on when the drum cartridge 10 has been set. The toner detect switch 9 is also a mechanical switch similarly operating.
When the cartridge is set to the printer, an earth voltage (corresponding to a low signal) is supplied to the I/O port 7. Accordingly, the setting of them can be detected through the check of the voltage supplied to the I/O port 7.
Thus, in the conventional laser beam printer, emission of the laser beam is prohibited until the drum cartridge 10 and the toner cartridge 11 as the parts located at the laser-beam shut-off place are set to the printer. Accordingly, the operators are protected from being exposed to laser beams.
As described above, in the conventional laser beam printer, the shut-off of the laser beam depends on the on/off o of the mechanical switch. During the repair and inspection of the printer after removal of the drum cartridge 10 and the like, the switch is often turned on mistakenly or any of other manner than the normal switching manner. In such a case, the operator will be exposed to dangerous laser beams.
During the inspection and repair, the switch is frequently turned on in a switching manner different from the normal switching manner. For example, when a bar shaped like the projection 21-2, already prepared, is applied to the switch (see FIG. 4), the switch is turned on. When the switch is turned on in this way and the laser emitting condition is unexpectedly set up, the laser beams will hit the operator. To solve the problem of the exposure of the operation to dangerous laser beams, the present invention is made.